1. Field of the Invention
The present invention relates to an illumination apparatus using a light guide.
2. Related Background Art
As a conventional image reading apparatus for reading an original image, there is a contact type image sensor which contacts with an original and scans the original to read an image. One example of an illumination apparatus for use in such contact type image sensor is shown in FIGS. 18, 19 and 20. FIG. 18 is a perspective view, FIG. 19 is a sectional view, and FIG. 20 is a view of an end surface viewed from a longitudinal direction.
In FIG. 18, light radiated from a light emitting element 1 such as LED as a light source disposed on an end surface 12 of a light guide 2 is incident upon the inside of the light guide 2, repeatedly reflected by the inner face of the light guide 2 and thereby guided in the longitudinal direction of the light guide 2. A part of the light guide 2 is provided with a diffusing surface 4 for diffusing and/or reflecting the light incident along the longitudinal direction. Then as shown in FIG. 19, when the light repeatedly reflected by the inner face in the longitudinal direction is incident upon the diffusing surface 4, the incident light is scattered, a part of the light radiates from a radiating surface 13 of the light guide 2, and contributes to the illumination of the original as illumination light.
However, in the above-described conventional illumination apparatus, since there is a large amount of light directly incident upon the diffusing surface in the vicinity of the light emitting element in the light guide, and the regular reflected light from the diffusing surface contributes as the illumination light to the object to be illuminated, the illuminance of the vicinity of the light emitting element is higher than that of other areas, and a problem arises that nonuniformity is caused in the illuminance of the longitudinal direction of the light guide.
Moreover, there is one example of a conventional contact type image sensor as shown in FIG. 21.
In FIG. 21, the light radiated from the light source 1 constituted of the light emitting elements such as LED disposed on the end surface of the light guide 2 is incident upon the inside of the light guide 2, repeatedly reflected by the inner face of the light guide 2 and thereby guided in the longitudinal direction of the light guide 2. A part of the light guide 2 is provided with the diffusing surface 4 along the longitudinal direction, the light repeatedly reflected by the inner face in the longitudinal direction is scattered upon incidence on the diffusing surface 4, and a part of the light contributes as the illumination light to illuminate the original.
Here, a light guide cover 3 as shown in FIG. 22 is disposed outside the light guide 2 to enhance the light utilization efficiency, and attached so as to cover the light guide via an air layer so that the light leaking from the light guide 2 in a direction different from the original irradiation direction is returned into the light guide. To this end, the light guide cover 3 is formed, for example, of a white material with high light reflecting properties. An original (not shown) positioned on a read line 6 is irradiated with the light radiated from a radiating surface 5 (the surface of the light guide 2 radiating the light which contributes to the lighting of the original as the object to be illuminated) of the light guide 2 in an opening 16 of the light guide cover 3, and the reflected light is formed into an image by a rod lens array 7 on a line sensor 11 disposed on a sensor array 9. When the line sensor 11 converts the information of the light formed into the image to an electric signal and outputs the signal, the reading of the original is carried out.
FIG. 23 is a view only showing the light guide 2 having LED 1 in its end portion and the light guide cover 3. Since the light guide cover 3 covering the light guide 2 is manufactured mainly by injection molding, one side in a metal mold extracting direction forms an opening to extract the metal mold. Therefore, the opening of the light guide cover 3 is larger than the radiating surface 5 of the light guide 2, and the light not contributing to the illumination of the original as the object to be illuminated leaks from the side surface 12 of the light guide 2, which is a large cause for a decrease of the light utilization efficiency.
An object of the present invention is to uniform an illuminance distribution of a longitudinal direction of a light guide in an illumination apparatus using the light guide.
To achieve the above-described object, according to one embodiment of the present invention, there is provided an illumination apparatus comprising a plurality of light sources, and a light guide for guiding light from the plurality of light sources in a longitudinal direction and radiating the light to illuminate an object to be illuminated, wherein the light guide comprises a diffuser for diffusing and/or reflecting the light from the plurality of light sources along the longitudinal direction of the light guide, and a radiator for radiating the light diffused and/or reflected by the diffuser in a predetermined direction, and wherein the diffuser and the radiator are arranged so that a normal line passing through the center of the width of the diffuser differs from the predetermined direction, and the plurality of light sources are arranged on the normal line, at least in the vicinity of the light sources when viewed from the end surface side of the longitudinal direction of the light guide.
Furthermore, by this constitution, the illuminance distribution of the longitudinal direction of the light guide can be uniformed.
Moreover, another object of the present invention is to enhance the utilization efficiency of the light radiated from the light guide.
To achieve the object, according to one embodiment of the present invention, there is provided a light guide built in a light guide cover comprising a light non-transmitting member and provided with a light transmitting member for guiding light from a light source in a longitudinal direction and radiating the light to illuminate the object to be illuminated, wherein a light leakage preventing portion for restricting light leakage is disposed in a portion other than a radiator for radiating the light in a predetermined direction in a portion exposed from the light guide cover.
By this constitution, the utilization efficiency of the light radiated from the light guide can be enhanced.
Other objects and advantages of the present invention will become apparent from the following specification and the accompanying drawings.